Method of controlling reverse transmission in a mobile communication system

ABSTRACT

A reverse transmission controlling method in a mobile communication system. After receiving forward information commanding a reverse data rate change on a forward channel from a base station, a mobile station increases its reverse data rate to a data rate equal to or lower than a maximum data rate if the forward information commands a reverse data rate increase, determines whether the increased data rate can be further increased for the next frame, and transmits the determination result with information representing the increased data rate to the base station.

PRIORITY

This application claims priority to an application entitled “Method ofControlling Reverse Transmission in a Mobile Communication System” filedin the Korean Industrial Property Office on Mar. 29, 2001 and assignedSer. No. 2001-16660, the contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a transmission controllingmethod in a mobile communication system, and in particular, to a methodof controlling reverse transmission.

2. Description of the Related Art

With the phenomenal growth of mobile communication technology, manydifferent mobile communication systems have been proposed and arecurrently being field-tested. These systems generally operate based onCDMA (Code Division Multiple Access) and a 1xEV-DO (1x Evolution-DataOnly) system called HDR (High Data Rate), designed to carry outhigh-rate data transmission dedicatedly.

Similarly to other systems, 1xEV-DO systems also require appropriatescheduling to efficiently transmit packet data on the forward andreverse links. “The forward link” is a link directed from a base stationto an access terminal (AT) and “a reverse link” is the opposite link.For forward data transmission, the base station transmits data to aparticular AT in the best channel condition, considering the air linkstatuses between the base station and 1xEV-DO ATs and otherenvironments, resulting in a maximized data transmission throughput forthe AT. Concerning reverse data transmission, a plurality of ATs accessthe base station simultaneously. In this situation, the base stationcontrols overload within reverse link capacity by appropriatelycontrolling congestion and data flows from the ATs.

Besides the 1xEV-DO systems, other mobile communication systems designedto support multimedia service must also manage reverse data transmissionefficiently. To do so, system performance and capacity must be ensured.

In the existing 1xEV-DO systems, an AT carries out reverse datatransmission based on an RAB (Reverse Activity Bit) and an RRL(ReverseRateLimit) message received from a base station, and tells thebase station its variable data rate via an RRI (Reverse Rate Indicator).The RRI indicates to the base station the data rate at which the reversetraffic data is being sent. The base station transmits the followingtime-multiplexed channels to the AT: a forward MAC (Medium AccessControl) channel, a pilot channel, an FAB (Forward Activity Bit) channeland an RAB channel. The RAB represents the congestion degree of thereverse link and a data rate available to the AT varies according to theRAB. The base station controls a data flow from the AT by commanding anincrease/decrease in the reverse data rate using the RAB to control theoverload and capacity of the reverse link. Since the RAB is broadcast toa plurality of ATs, the ATs receiving the RAB increase their data ratesor reduce them uniformly according to the RAB. The transmission time (ortransmission period) of the RAB is determined by Equation (1):T mod RABlength  (1)where T is system time and RABlength is the length of the RAB expressedin the number of slots. Table 1 below lists binary values representingRAB lengths. The base station transmits one of the binary values to theATs and then the ATs calculate a slot time they receive the RAB on aforward MAC channel (F-MAC channel) using the received RABlengthinformation and the system time.

TABLE 1 Binary Length (slots) 00  8 01 16 10 32 11 64

An AT receives a persistence vector defined in a message from the basestation at or during a connection. When RAB=0, the persistence vector isset to increase the reverse data rate and when RAB=1, it is set todecrease the reverse data rate. Using the persistence vector, the ATperforms a persistence test. If the persistence test is passed, the ATwill either increase the reverse data rate or reduce it. If thepersistence test is failed, then the AT maintains the reverse data rate.

To describe in detail, if the RAB is 0 and the persistence test ispassed, the reverse data rate is increased. On the contrary, if the RABis 1 and the persistence is passed, the reverse data rate is reduced.The success or failure of the persistence test depends on whether agenerated random number satisfies a desired condition. Since the reversedata rate varies with uncertainty in probability terms, the base stationdoes not know how many ATs increase/decrease their data rates. Timedelay occurs on the reverse link until a high capacity state istransitioned to a full utilization state. In the reverse link fullutilization state, overload and underload alternate. However, the basestation cannot know how serious the overload or underload conditionbecause the base station simply transmits an RAB and the ATsincrease/decrease their data rates according to the results ofpersistence tests.

If the overload condition becomes serious, it leads to the increase ofreverse data loss. On the other hand, if the underload condition becomesserious, the use efficiency of reverse channels is dropped. Therefore,there is a need for exploring a method of rapidly reaching the reverselink full utilization state and a method of increasing the useefficiency of reverse channels, while preventing the occurrence ofoverload in the base station.

FIG. 1 is a flowchart illustrating a reverse data rate controllingprocedure for an AT in an existing 1xEV-DO system.

The AT sets its lowest available data rate at an initial reverse datatransmission. If the current data rate is lower than a data rateprovided in an RRL message received from a base station, the ATtransmits data at the provided data rate after 32 slots (53.33ms). Onthe other hand, if the current data rate is higher than the provideddata rate, the AT transmits data at the provided data rate. For thesubsequent reverse transmission, the AT determines its data rate by theprocedure illustrated in FIG. 1. The RRL message is transmitted to theAT in determining an initial reverse data rate and resetting the reversedata rate.

After determining its data rate, the AT reports its data rate to thebase station by an RRI symbol as shown in Table 2. The reverse data rateis selected among 4.8, 9.6, 19.2, 38.4, 76.8 and 153.6 kbps. Thisreverse data rate is reset by a message such as an RRL message or an RABmessage received from the base station. Table 2 below lists RRI mappingsin the 1xEV-DO system.

TABLE 2 Data rate (kbps) RRI symbol  4.8 001  9.6 010 19.2 011 38.4 10076.8 101 153.6  110

The base station determines the data rate of the AT from the RRI symbolsas shown in Table 2 and controls the AT to reset its data rate. To aidthe AT in resetting its data rate, the base station should transmit anRRL message as shown in Table 3 to the AT.

TABLE 3 Field Length (bits) Message ID 8 29 occurrences of the followingtwo fields RateLimitIncluded 1 RateLimit 0 or 4 Reserved Variable

The RRL message is forward directed to control a reverse data rate. Uponreceipt of the RRL message, the AT resets the reverse data rate bycomparing the current reverse data rate with a data rate set in the RRLmessage. 29 records may be inserted in the above RRL message and eachrecord indicates a data rate assigned to a corresponding MACindex amongMACindexes 3 to 31. In Table 3, Message ID indicates the ID of the RRLmessage. RateLimitlncluded is a field indicating whether RateLimit isincluded in the RRL message. If RateLimit is included, RateLimitlncludedis set to 1 and otherwise, it is set to 0. RateLimit indicates a datarate assigned to a corresponding AT. The base station assigns data ratesshown in Table 4 to ATs using four bits.

TABLE 4 0 × 0  4.8 kbps 0 × 1  9.6 kbps 0 × 2 19.2 kbps 0 × 3 38.4 kbps0 × 4 76.8 kbps 0 × 0 153.6 kbps  All other values are invalid

During reverse data transmission, the AT monitors a F-MAC channel fromthe base station, especially the RAB on the F-MAC channel, and adjustsits current data rate by performing a persistence test.

Referring to FIG. 1, the AT monitors the RAB of an F-MAC channel from abase station included in the active set of the AT in step 100 anddetermines whether the RAB is 1 in step 102. If the AT has sixsectors/base stations in its active set, it determines whether at leastone of the RABs of the F-MAC channels received from the six sectors/basestations is 1. If at least one RAB is 1, the AT proceeds to step 112 andotherwise, it goes to step 104.

The case where all RABs=0 will be considered first.

If the RAB is 0, the AT performs a persistence test in step 104. Thepersistence test is available when the base station broadcasts the RABto a plurality of ATs to control the amount of reverse data from theATs. The persistence test is passed or failed depending on whether agenerated random number satisfies a desired condition.

If the persistence test is passed in step 104, the AT increases its datarate (TX rate) in step 106. On the contrary, if the persistence test isfailed, the AT jumps to step 120. The AT increases the TX rate in step106 and compares the increased TX rate with a maximum allowed data rate(a max TX rate) in step 108. If the increased TX rate is higher than themax TX rate, the AT sets the TX rate to the max TX rate in step 110 andgoes to step 120. If, in step 108, the increased TX rate is not higherthan the max TX rate, the AT goes directly to step 120

Now, the case where at least one RAB=1 will be considered.

If the RAB is 1 in step 102, the AT performs a persistence test in step112. If the persistence test is failed, the AT jumps to step 120. If thepersistence test is passed, the AT decreases the TX rate in step 114 andcompares the decreased TX rate with a minimum data rate (a min TX rate)in step 116. If the decreased TX rate is lower than the min TX rate, theAT goes to step 118 and otherwise, it jumps to step 120. The AT sets theTX rate to the min TX rate in step 118 and goes to step 120. The min TXrate can be a default data rate of 9.6 kbps or a data rate designated bysome message at a call connection.

In step 120, the AT generates an RRI symbol corresponding to the set TXrate. The AT transmits the RRI symbol along with traffic data only if atraffic connection is opened between the base station and the AT. If thetraffic connection is not opened, it transmits only the RRI symbol.

FIG. 2 is a diagram illustrating data transmission/reception between anAT and an HDR sector included in the active set of the AT. Asillustrated in FIG. 2, F- and R-traffic channels, and F- and R-MACchannels have been established between the AT and sector 1 with aconnection opened between them. No F-traffic channels are assigned tothe AT from sector 2 (up to sectors 2 to 6) with no connection openedbetween them. In the 1xEV-DO system, the AT can maintain up to sixsectors/base stations in its active set. Therefore, to determine its TXrate, the AT monitors F-MAC channels from all the sectors of the activeset, especially RABs on the F-MAC channels.

Upon receipt of at least one RAB set to 1, the AT performs a persistencetest to decrease its TX rate. In the persistence test, the AT generatesa random number and compares it with a persistence vector defined by thebase station at or during a connection. If the random number satisfies adesired condition, the AT determines that the persistence test ispassed. The AT then decreases the TX rate. On the contrary, if thepersistence test is failed, the AT maintains the TX rate. If the TX rateis lower than a min TX rate, the AT sets the TX rate at the min TX rate.Meanwhile, if all the RABs are set to 0 and a persistence test ispassed, then the TX rate is increased. If the persistence test isfailed, the AT maintains the TX rate. If the TX rate becomes higher thana max TX rate, the AT sets the TX rate to the max TX rate. Also, in thecase where the AT is limited in transmission power, it maintains the TXrate. The RAB that functions to increase a reverse data rate or reducesit is broadcast to ATs in TDM with an FAB on a forward common channel,i.e., a F-MAC channel. The ATs increase/decrease their data ratesuniformly according to the RAB.

From the system's perspective, the above-described reverse transmissioncontrolling method for the current 1xEV-DO systems simplifies bandwidthcontrol and overhead control. However, the uniform control withoutconsidering the individual statuses of ATs brings about a bandwidthwaste and decreases the data transmission efficiency of the ATs.

Moreover, a long time delay is involved in reaching a full utilizationstate on the reverse link, resulting in the decrease of channel useefficiency. The occurrence of an overload may lead to reverse data loss.As a result, communication quality is deteriorated.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a methodof rapidly reaching the full utilization state of a reverse link.

It is another object of the present invention to provide a method ofincreasing the use efficiency of a reverse link.

It is a further object of the present invention to provide a method ofpreventing the occurrence of an overload on a reverse link.

The foregoing and other objects of the present invention are achieved byproviding a reverse transmission controlling method in a mobilecommunication system. After receiving forward information commanding areverse data rate change on a forward control channel from a basestation, a mobile station increases its data rate to be equal to orlower than a maximum data rate if the forward information commands areverse data rate increase, determines whether the increased data ratecan be further increased for the next frame, and transmits thedetermination result with information representing the increased datarate to the base station.

If the forward information commands a conditional reverse data rateincrease, the mobile station increases its data rate to be equal to orlower than a maximum data rate based on information indicating whether adata rate increase is available that is determined at the previous frametransmission. Then, the mobile station determines whether the increaseddata rate can be further increased for the next frame and transmits thedetermination result with information representing the increased datarate to the base station.

If the forward information commands a conditional data rate decrease,the mobile station decreases its data rate to be equal to or higher thana minimum data rate based on information determined at the previousframe transmission indicating whether a data rate increase is available.Then, the mobile station determines whether the decreased data rate canbe increased for the next frame and transmits the determination resultwith information representing the increased data rate to the basestation.

If the forward information commands an unconditional data ratemaintenance, the mobile station maintains its data rate. Then, themobile station determines whether the maintained reverse data rate canbe increased for the next frame and transmits the determination resultwith information representing the increased data rate to the basestation.

The forward information is an extended RAB. If the forward informationis received from at least two base stations, a control RAB is generatedfrom extended RABs received from the base stations. Changing the reversedata rate is determined based on the control RAB.

If at least one of the extended RABs indicates a conditional decrease,the control RAB is set to indicate a conditional decrease. If none ofthe extended RABs indicate a conditional decrease and at least one ofthe extended RABs indicates an unconditional data rate maintenance, thecontrol RAB is set to indicate an unconditional data rate maintenance.If none of the extended RABs indicate either a conditional decrease oran unconditional data rate maintenance and at least one of the extendedRABs indicates a conditional increase, the control RAB is set toindicate a conditional increase. Finally, if all the extended RABsindicate an unconditional increase, the control RAB is set to indicatean unconditional increase.

After receiving reverse information indicating whether a reverse datarate increase is available for the next reverse frame from a mobilestation, a base station determines the highest data rate allowed to themobile station by mobile station acquisition and characteristicanalysis, generates a reverse data rate value, transmits informationrepresenting the highest data rate and the reverse data rate value tothe mobile station, determines an extended RAB based on the receivedreverse information and the current capacity of a reverse link, andtransmits the extended RAB to the mobile station.

If the reverse link is in an overload state, the extended RAB is set toindicate a conditional data rate decrease. If an increase in the datarates of all mobile stations within the coverage area of the basestation does not cause overload on the reverse link, the extended RAB isset to indicate an unconditional data rate increase. If the reverse linkis not in an overload state and can accommodate an increase in the datarates of all the mobile stations, the extended RAB is set to indicate aconditional data rate increase. Finally, if the reverse link is not inan overload state and cannot accommodate an increase in the data ratesof all the mobile stations, the extended RAB is set to indicate anunconditional data rate maintenance.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a flowchart illustrating a reverse data rate controllingmethod for a mobile station in a conventional mobile communicationsystem;

FIG. 2 is a diagram illustrating data transmission/reception between amobile station and a sector included the active set of the mobilestation;

FIGS. 3A to 3F are flowcharts illustrating a reverse data ratecontrolling method for a mobile station in a data transmission systemaccording to an embodiment of the present invention;

FIG. 4 is a flowchart illustrating a reverse data rate controllingmethod for a base station in the data transmission system according tothe embodiment of the present invention; and

FIG. 5 is a flowchart illustrating a method of generating an extendedRAB for control of reverse data rates in the base station in the datatransmission system according to the embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail since they would obscure the invention inunnecessary detail.

The present invention provides a reverse data rate controlling methodfor a mobile station (MS) and new RAB and new RRI structures forsupporting the method in a system and a novel high rate datatransmission system according to the present invention. A base stationoperation for supporting the reverse data rate controlling method isalso provided. The new RAB and new RRI according to the presentinvention will be hereinafter referred to as an extended RAB and anextended RRI, respectively.

The extended RAB is given in Table 5.

TABLE 5 RAB Operation of MS 00 Increase reverse link data rate dependingon increase previous persistence pre-test 01 Decrease reverse link datarate depending on decrease persistence test 10 Increase reverse linkdata rate 11 Keep current reverse link data rate

A 1-bit RAB simply represents the increase or decrease of a reverse datarate in the conventional system, whereas the extended RAB shown in Table5 represents the increase, maintenance, and decrease of a reverse datarate in the present invention.

(1) Extended RAB=00

A mobile station increase its data rate, only if it passed its previousincrease persistence pre-test for a data rate increase in the previousframe. In this case, the reverse data rate increase is conditional.

(2) Extended RAB=01

A mobile station reduces its data rate, only if it has passed a decreasepersistence test for a data rate decrease. In this case, the reversedata rate decrease is conditional.

(3) Extended RAB=10

All mobile stations increase their data rates regardless of theirprevious increase persistence pre-tests. That is, the reverse data ratesare unconditionally increased.

(4) Extended RAB=11

All mobile stations keep their data rates regardless of their previousincrease persistence pre-tests. That is, the reverse data rates areunconditionally maintained.

FIGS. 3A to 3F are flowcharts illustrating a reverse data ratecontrolling method for a mobile station in a data transmission systemaccording to an embodiment of the present invention. Referring to FIGS.3A to 3F, the mobile station monitors extended RABs received on F-MACchannels from all base stations in its active set in step 300. Only thereverse data rates that are defined by RRI symbols are available. Themobile station can maintain up to six sectors/base stations in itsactive set. An active set is a set of sectors/base station serving amobile station. If a connection is opened between the mobile station anda base station in the active set, F- and R-traffic channels and areverse power control channels are assigned to the mobile station. Withno connection opened, the mobile station monitors only a control channelfrom the base station. The mobile station determines “a control RAB”according to a received extended RAB as follows.

(Conditions)

(1) If at least one of the extended RABs received from all of the basestations in the active set is 01, the control RAB is set to 01;

(2) If none of the extended RABs received from all of the base stationsin the active set are 01 and at least one of them is 11, the control RABis set to 11;

(3) If none of the extended RABs received from all of the base stationsin the active set are either 01 or 11 and at least one of them is 00,the control RAB is set to 00; and

(4) If all of the extended RABs received from all of the base stationsin the active set are 10, the control RAB is set to 10.

The control RAB set under the above conditions has a great influence onthe capacity of a sector in the case of a reverse data rate increase.

The mobile station checks the control RAB in steps 302 to 306. If thecontrol RAB is 00, the mobile station determines whether its previousincrease persistence pre-test was passed by checking a variablePreTestRes representing the result of the increase persistence pre-test,that is, whether PreTestRes=0 in step 310 in FIG. 3 b. If the previousincrease persistence pre-test was passed, the mobile station goes tostep 312 and otherwise, it jumps to step 318. The mobile stationincreases its TX rate in step 312 and compares the increased TX ratewith a max TX rate in step 314. If the increased TX rate is higher thanthe max TX rate, the mobile station proceeds to step 316 and otherwise,it goes to step 318. In step 316 the mobile station sets the TX rate tothe max TX rate and goes to step 318. Thus, the TX rate is completelyset.

In step 318, the mobile station performs an increase persistencepre-test to control the reverse TX rate for the next frame. If theincrease persistence pre-test is passed, the mobile station sets thevariable PreTestRes to 0 in step 320 and selects and transmits an RRIsymbol representing the set TX rate in step 380 in FIG. 3 f. On thecontrary, if the increase persistence pre-test is failed, the mobilestation sets the variable PreTestRes to 1 in step 322 and selects andtransmits an RRI symbol representing the set TX rate in step 382 in FIG.3 f.

The mobile station determines that the increase persistence pre-test isfailed regardless of its real implementation in the case where the TXrate is limited by an RRL message that provides a maximum allowed datarate to each mobile station, when the mobile station has too limitedtransmission power to increase the TX rate, or the amount of data storedin a buffer is a threshold or less (i.e., the stored data can betransmitted without increasing the TX rate).

Table 6 lists RRI mappings to reverse data rates according to thepresent invention.

TABLE 6 Data Extended RRI symbol Extended RRI symbol rate (Increasepersistence pre-test (Increase persistence pre-test (kbps) success)failure) 0 0000 N/A 9.6 0001 1001 19.2 0010 1010 38.4 0011 1011 76.80100 1100 153.6 0101 1101 307.2 0110 1110 614.4 0111 1111 1024 N/A 1000

The extended RRI listed in Table 6 are a modification from theconventional RRI to indicate to the base station at what rate thereverse data is being sent. Based on the acquired reverse data rate, thebase station recovers the original reverse data. The extended RRI isdesigned to represent the reverse data rates defined by the 1xEVDVsystems with PreTestRes set in the first field.

If the control RAB is 01 in step 304, the mobile station performs adecrease persistence test in step 330 in FIG. 3 c. If the decreasepersistence test is passed, the mobile station goes to step 332 andotherwise, it jumps to step 338. The mobile station decreases its TXrate in step 332 and compares the decreased TX rate with a min TX ratein step 334. If the decreased TX rate is lower than the min TX rate, themobile station proceeds to step 336 and otherwise, it goes to step 338.In step 336 the mobile station sets the TX rate to the min TX rate andgoes to step 338.

In step 338, the mobile station performs an increase persistencepre-test to control the reverse TX rate for the next frame. If theincrease persistence pre-test is passed, the mobile station sets thevariable PreTestRes to 0 in step 340, and selects an RRI symbolrepresenting the set TX rate from a table such as Table 6 and transmitsthe selected RRI symbol in step 380 in FIG. 3 f. On the contrary, if theincrease persistence pre-test is failed, the mobile station sets thevariable PreTestRes to 1 in step 342, and selects an RRI symbolrepresenting the set TX rate from a table such as Table 6 and transmitsthe selected RRI symbol in step 382 in FIG. 3 f.

The mobile station sets the variable PreTestRes to 1, determining thatthe increase persistence pre-test is failed regardless of its realimplementation in the case where the TX rate is limited by an RRLmessage, when the mobile station has too limited transmission power toincrease the TX rate, or the amount of data stored in a buffer is athreshold or less.

If the control RAB is not 10 in step 306, then the RAB must be 11. Thisimplies that the current TX rate is supposed to be maintained. Hence, instep 370, the mobile station checks the variable PreTestRes representingthe result of the previous increase persistence test, which wasperformed to report the reverse link condition for the previous frame inFIG. 3 e. If PreTestRes is 0, that is, a TX rate increase is available,the mobile station performs an increase persistence pre-test to controlthe reverse TX rate for the next frame in step 372. If the increasepersistence pre-test is passed, the mobile station sets the variablePreTestRes to 0 in step 374, and selects an RRI symbol representing theset TX rate from a table such as Table 6 and transmits the selected RRIsymbol in step 380 in FIG. 3 f.

On the other hand, if PreTestRes is 1 in step 370 or if the increasepersistence pre-test is failed in step 372, the mobile station sets thevariable PreTestRes to 1 in step 376, and selects an RRI symbolrepresenting the set TX rate from a table such as Table 6 and transmitsthe selected RRI symbol in step 382 in FIG. 3 f. The reason forperforming an increase persistence pre-test only in a mobile stationwith PreTestRes=0 despite a TX rate maintenance command by an extendedRAB is to preserve the reverse link capacity.

FIG. 4 is a flowchart illustrating a reverse data rate controllingmethod for a base station in the high rate data transmission systemaccording to the embodiment of the present invention.

Referring to FIG. 4, upon receipt of connection open requests frommobile stations, the base station carries out mobile station acquisitionin step 400 and analyzes the characteristics of the mobile stations instep 402. In step 404, the base station analyses the characteristics ofreverse traffic received from the mobile stations, that is, determinesQoS (Quality of Service) of packet data services requested by the mobilestations. In steps 406, the base station sets MACindex fields by whichthe mobile stations are identified. The base station sets RateLimitfields that limit the data rates of the mobile stations based on thecharacteristics of the mobile stations and their application services instep 408. Then the base station assembles the RRL message with MessageID and other related message fields for transmission in the air in step412 and transmits the RRL message to the mobile stations in step 414.

In step 416, the base station receives PreTestRes information indicatingwhether a reverse data rate increase is available for the next framesfrom the mobile stations and analyzes the PreTestRes information. Thebase station checks the current reverse channel conditions and generatesan RAB according to the reverse channel conditions in step 418 andbroadcasts the RAB to the mobile stations in step 420. If one RAB is setfor each mobile station, the RAB may not be broadcast but must betransmitted to only the corresponding mobile station.

FIG. 5 is a flowchart illustrating a method of generating an extendedRAB for control of reverse data rates in the base station in the ratedata transmission system according to the embodiment of the presentinvention.

Referring to FIG. 5, the base station determines whether the reverselink is currently in an overload state in step 500. In an overloadstate, the base station sets the extended RAB to 01 in step 512. Thisimplies that a corresponding mobile station sets a control RAB to 01 anddecreases its TX rate according to a decrease persistence test.

If the current reverse link is not in an overload state in step 500, thebase station determines whether the current reverse link is a low loadstate in step 502. In a low load state, the base station sets theextended RAB to 10.

If the current reverse link is not in a low load state in step 502, thebase station checks PreTestRes information received from mobile stationsto determine whether overload will occur at the next reversetransmission in step 504. If overload is expected, the base station setsthe extended RAB to 11 in step 508. If no overload is expected, the basestation sets the extended RAB to 00 in step 506. The set extended RAB isbroadcast or transmitted to a corresponding mobile station only.

While the embodiment of the present invention has been described in thecontext that one mobile station uses one radio traffic channel, it canbe further contemplated in other embodiments that one mobile stationuses two radio traffic channels.

1) Use of one 2-bit RAB and one 7-bit RRI symbol.

By representing each of the data rates of the two reverse trafficchannels using one bit of the RAB, the data rates areincreased/maintained/decreased simultaneously. The result of an increasepersistence pre-test is represented by one bit of the RRI symbol (e.g.,MSB). Three of the remaining bits of the RRI symbol are assigned to thedata rate of a first reverse traffic channel and the other three bits,to the data rate of a second reverse traffic channel. The reverse datarates are increased/decreased according to the result of the increasepersistence pre-test on the two reverse traffic channels and the commonRAB.

(2) Use of one 2-bit RAB and one 8-bit RRI symbol.

While the RAB applies commonly to the two reverse traffic channels, anincrease persistence pre-test is performed independently for each of thereverse traffic channels. Therefore, the reverse data rates are changedindividually. Two bits of the RRI symbol are assigned to the respectiveresults of the increase persistence pre-tests for the reverse trafficchannels. The other six bits of the RRI symbol are equally separated tobe assigned to the data rates of the reverse traffic channels. Thereverse data rates are increased/decreased according to the results ofthe increase persistence pre-tests and the common RAB.

(3) Use of Two 2-bit RABs and one 7-bit RRI symbol.

One RAB is assigned for each of the reverse traffic channel. Thus, thedata rates of the reverse traffic channels are changed individually. Oneincrease persistence pre-test is performed for the two reverse trafficchannels. Here a decrease persistence test can be performed commonly forthe reverse traffic channels or independently for each of the reversetraffic channels. The RRI symbol is used in the same manner as the case(1). The reverse data rates are increased/decreased according to theresult of the common increase persistence pre-test and the RABs.

(4) Use of two 2-bit RABs and one 8-bit RRI symbol.

One RAB is assigned for each of the reverse traffic channels and anincrease persistence pre-test is also performed independently for eachof the reverse traffic channels. The RRI symbol is used in the samemanner as the case (2). The two reverse traffic channels are separatelycontrolled.

The result(s) of the increase persistence pre-test(s) may be transmittedon a channel other than an RRI channel (e.g., a RICH) or on a newdefined channel. While its transmission period is set preferably on aframe basis, it can be set in any other manner.

In accordance with the present invention as described above, mobilestations determine whether a reverse data rate increase is available forthe next reverse transmission and tell a base station the determinationresults. Then the base station carries out a planned reverse linkcontrol for the next reverse transmission. Therefore, the occurrence ofan overload is prevented, reverse data loss is minimized, and thetransmission efficiency of the reverse link is maximized.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A method of controlling a reverse data rate in a mobile station afterreceiving forward information commanding a reverse data rate change on aforward channel from a base station, the forward information indicatingone of an increase, decrease, and maintenance of the reverse data rate,the method comprising the steps of: increasing, by the mobile station,the reverse data rate to be equal to or lower than a maximum data rateif the forward information commands a reverse data rate increase; anddetermining, by the mobile station, whether the increased data rateaccording to the received forward information is increasable for a nextframe and transmitting the determination result to the base station. 2.The method of claim 1, wherein the forward information is an extendedreverse activity bit (RAB).
 3. The method of claim 2, wherein if theforward information is received from at least two base stations, acontrol RAB is generated from extended RABs received from the basestations, and a change in the reverse data rate is determined based onthe control RAB.
 4. The method of claim 3, wherein: if at least one ofthe extended RABs indicates a conditional decrease, the control RAB isset to indicate the conditional decrease; if none of the extended RABsindicate the conditional decrease and at least one of the extended RABsindicates an unconditional data rate maintenance, the control RAB is setto indicate the unconditional data rate maintenance; if none of theextended RABs indicate either the conditional decrease or theunconditional data rate maintenance and at least one of the extendedRABs indicates a conditional increase, the control RAB is set toindicate the conditional increase; and if all the extended RABs indicatean unconditional increase, the control RAB is set to indicate theunconditional increase.
 5. A method of controlling a reverse data ratein a mobile station after receiving forward information commanding areverse data rate change on a forward channel from a base station, theforward information indicating one of an increase, decrease, andmaintenance of the reverse data rate, the method comprising the stepsof: increasing, by the mobile station, the reverse data rate to be equalto or lower than a maximum data rate based on information indicatingwhether a data rate increase is available that is determined at aprevious frame transmission if the forward information commands aconditional reverse data rate increase; and determining, by the mobilestation, whether the increased data rate according to the receivedforward information is increasable for a next frame and transmitting thedetermination result to the base station.
 6. The method of claim 5,wherein the forward information is an extended reverse activity bit(RAB).
 7. The method of claim 6, wherein if the forward information isreceived from at least two base stations, a control RAB is generatedfrom extended RABs received from the base stations and a change in thereverse data rate is determined based on the control RAB.
 8. The methodof claim 7, wherein: if at least one of the extended RABs indicates aconditional decrease, the control RAB is set to indicate the conditionaldecrease; if none of the extended RABs indicate the conditional decreaseand at least one of the extended RABs indicates an unconditional datarate maintenance, the control RAB is set to indicate the unconditionaldata rate maintenance; if none of the extended RABs indicate either theconditional decrease or the unconditional data rate maintenance and atleast one of the extended RABs indicates a conditional increase, thecontrol RAB is set to indicate the conditional increase; and if all theextended RABs indicate an unconditional increase, the control RAB is setto indicate the unconditional increase.
 9. A method of controlling areverse data rate in a mobile station after receiving forwardinformation commanding a reverse data rate change on a forward channelfrom a base station, the forward information indicating one of anincrease, decrease, and maintenance of the reverse data rate, the methodcomprising the steps of: decreasing, by the mobile station, the reversedata rate to be equal to or higher than a minimum data rate based oninformation indicating whether a data rate increase is available that isdetermined at a previous frame transmission if the forward informationcommands a conditional data rate decrease; and determining, by themobile station, whether the decreased data rate according to thereceived forward information is decreasable for a next frame andtransmitting the determination result to the base station.
 10. Themethod of claim 9, wherein the forward information is an extendedreverse activity bit (RAB).
 11. The method of claim 10, wherein if theforward information is received from at least two base stations, acontrol RAB is generated from extended RABs received from the basestations and a change in the reverse data rate is determined based onthe control RAB.
 12. The method of claim 11, wherein: if at least one ofthe extended RABs indicates a conditional decrease, the control RAB isset to indicate the conditional decrease; if none of the extended RABsindicate the conditional decrease and at least one of the extended RABsindicates an unconditional data rate maintenance, the control RAB is setto indicate the unconditional data rate maintenance; if none of theextended RABs indicate either the conditional decrease or theunconditional data rate maintenance and at least one of the extendedRABs indicates a conditional increase, the control RAB is set toindicate the conditional increase; and if all the extended RABs indicatean unconditional increase, the control RAB is set to indicate theunconditional increase.
 13. A method of controlling a reverse data ratein a mobile station after receiving forward information commanding areverse data rate change on a forward channel from a base station, theforward information indicating one of an increase, decrease, andmaintenance of the reverse data rate, the method comprising the stepsof: maintaining, by the mobile station, the reverse data rate if theforward information commands an unconditional data rate maintenance; anddetermining, by the mobile station, whether the maintained reverse datarate according to the received forward information is maintainable for anext frame and transmitting the determination result to the basestation.
 14. The method of claim 13, wherein the forward information isan extended reverse activity bit (RAB).
 15. The method of claim 14,wherein if the forward information is received from at least two basestations, a control RAB is generated from extended RABs received fromthe base stations and a change in the reverse data rate is determinedbased on the control RAB.
 16. The method of claim 15, wherein: if atleast one of the extended RABs indicates a conditional decrease, thecontrol RAB is set to indicate the conditional decrease; if none of theextended RABs indicate the conditional decrease and at least one of theextended RABs indicates an unconditional data rate maintenance, thecontrol RAB is set to indicate the unconditional data rate maintenance;if none of the extended RABs indicate either the conditional decrease orthe unconditional data rate maintenance and at least one of the extendedRABs indicates a conditional increase, the control RAB is set toindicate the conditional increase; and if all the extended RABs indicatean unconditional increase, the control RAB is set to indicate theunconditional increase.
 17. The method of claim 13, wherein if it isdetermined at a frame transmission before the forward information isreceived that a reverse data rate increase is not available, nodetermination is made as to whether the maintained reverse data rate canbe increased for the next frame and a value which the reverse data rateis not available at the previous frame transmission is transmitted tothe base station.
 18. A method of controlling the data rate of a mobilestation in a base station comprising the steps of: determining, by themobile station, an extended reverse activity bit (RAB) based on reverseinformation received from the mobile station indicating whether areverse data rate increase is available for a next reverse frame and acurrent capacity of a reverse link and transmitting the extended RAB tothe mobile station, the RAB indicating one of an increase, decrease, andmaintenance of the reverse data rate.
 19. The method of claim 18,wherein: if the reverse link is in an overload state, the extended RABis set to indicate a conditional data rate decrease; if an increase inthe data rates of all mobile stations within a coverage area of the basestation does not cause an overload on the reverse link, the extended RABis set to indicate an unconditional data rate increase; if the reverselink is not in an overload state and can accommodate the increase in thedata rates of all the mobile stations, the extended RAB is set toindicate a conditional data rate increase; and if the reverse link isnot in the overload state and cannot accommodate the increase in thedata rates of all the mobile stations, the extended RAB is set toindicate an unconditional data rate maintenance.
 20. A mobile stationdevice for controlling a reverse data rate after receiving forwardinformation commanding a reverse data rate change on a forward channelfrom a base station, the forward information indicating one of anincrease, decrease, and maintenance of the reverse data rate, the devicecomprising: an apparatus for increasing the reverse data rate to equalto or lower than a maximum data rate if the forward information commandsa reverse data rate increase, increasing the reverse data rate to equalto or lower than the maximum data rate based on information determinedat a previous frame transmission indicating whether a data rate increaseis available if the forward information commands a conditional reversedata rate increase, decreasing the reverse data rate to equal to orhigher than a minimum data rate based on the information determined atthe previous frame transmission indicating whether a data rate increaseis available if the forward information commands a conditional reversedata rate decrease, maintaining the reverse data rate if the forwardinformation commands an unconditional data rate maintenance, anddetermining whether the changed or maintained reverse data rate can beincreased for a next frame; and an apparatus for transmitting thedetermination result to the base station.
 21. A base station device forcontrolling a data rate of a mobile station comprising: an apparatus fordetermining an extended reverse activity bit (RAB) based on reverseinformation received from the mobile station indicating whether areverse data rate increase is available for a next reverse frame and acurrent capacity of a reverse link, the RAB indicating one of anincrease, decrease, and maintenance of the reverse data rate; and anapparatus for transmitting the extended RAB to the mobile station.